A telecommunications network of this type is illustrated by way of example in FIG. 1. In FIG. 1, the telecommunications network is connected to an access computer AP of a data network DN, e.g. the Internet. Various subscriber terminals, e.g. a personal computer PC, a corded telephone TF and a cordless handset SL with its base station BS, are connected to a switching center VST. The switching center has a connection to the access computer AP of the data network DN via a circuit-switched public telephone network PSTN or via a packet-switched data network PN, e.g. X.25. At the same time, the public telephone network is connected to a mobile communications network PLMN which encompasses a plurality of radio devices RBS for connecting a plurality of subscriber terminals via a radio interface. Such subscriber terminals are, for example, mobile stations MS. It is also possible for a laptop LT or a personal computer to be connected to one of the indicated mobile stations via a serial interface, or for a mobile station to be integrated in a laptop or personal computer.
Given a network constellation of this type, the situation is currently as follows: A subscriber of the telecommunications network has various subscriber terminals, for example as illustrated in FIG. 1, which enable access to a data network, e.g. the Internet. Accordingly, with his subscriber terminal having display screen, e.g. TF, the subscriber can receive, read and process electronic mail (email) from the data network. It is assumed that the subscriber has established a data link to the data network with such a subscriber terminal in order to send his electronic mail from a so-called mail server, (not shown in FIG. 1) of the data network to his subscriber terminal. However, large items of electronic mail received which contain, for example, attachments in the format of PC applications (e.g. Word) cannot be displayed on the subscriber terminal, e.g. TF, because of the relatively small display and the low memory capacity. The subscriber therefore would like to use his personal computer to read such electronic mail. Hence, the subscriber must either establish a further data link (e.g. by using the second B-channel in the case of an ISDN connection) or a new data link to the access computer of the data network. Authorization must be obtained again, by typing in a password for example, the respective PC application must be activated for reading electronic mail on his PC, and the appropriate electronic mail with the attachment for displaying on the screen of the personal computer must be selected. If the subscriber then switches off the personal computer and would like to continue processing further electronic mail on his telephone with display, he must repeat the procedure set out above.
Also, in the case of Internet applications other than electronic mail, such as the accessing of provider pages with the aid of a so-called browser for example, the subscriber must proceed in a similar manner to reach the same state on his personal computer as was previously present on his telephone. That is, for example the same provider page accessed, the same state of transactions already made, such as a file transfer for example, the same bookmarks etc.
A procedure of this type is disadvantageous for at least the following reasons:                The establishment of a further or a new data link requires renewed authorization of the user, for example by entering passwords, and the selection of the access computer to be dialed.        The renewed connection establishment is in itself time-consuming since it is necessary to assign a new data network address (IP address) to the subscriber terminal (the personal computer in the example) for an Internet session, for which the so-called PPP (point-to-point) protocol is preferably used. Moreover, the communication partners of the data link must agree on transmission parameters, such as transmission bandwidth and quality for example, and also exchange authorization data again.        